PubMed · 435679
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M J Harrison. 1979. The normal fundus.. https://pubmed.ncbi.nlm.nih.gov/435679/
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If defined as diameter of image/diameter of object, the magnification M of the eye-camera system is kB, where k is a camera constant and B represents the vergence of the internal axis of the eye. The magnification may be assessed (1) from the length l of the eye, using the formula 1.336 k/(l-0.0016); (2) from the glass refraction G, using the formula kD/(1-G/D), in which D is the "normal" refractive power of the eye; or (3) from the principal point refraction A and the deviation delta D1 from the "normal" refractive power of the cornea, using the formula kD.(1 + delta B/D), where delta B = A + 0.84 delta D1. If k is 0.042 m, as in the Zeiss camera, and D is about 60 dpt, the formulas may be written as (1) M = 0.056/(l-0.0016); (2) M = 2.5/(1-0.017 G); and (3) M = 2.5.(1 + 0.017 delta B).
PURPOSE: The study was designed to compare the severity of age-related maculopathy as graded from photographs taken using three different techniques. METHODS: Two methods of nonstereoscopic 45 degrees retinal photography of the macula (through a nonpharmacologically dilated pupil and through a pharmacologically dilated pupil) were compared with results from standard 30 degrees stereoscopic photographs in 112 subjects. Corresponding photographic fields were graded by a masked grader for the presence of any drusen, soft drusen, retinal pigment epithelial degeneration, increased retinal pigmentation, and early and late age-related maculopathy. RESULTS: Exact agreement between gradings of the 45 degrees photographs taken through nonpharmacologically dilated pupils and 30 degrees photographs taken through dilated pupils was 75% for any drusen, 72% for soft drusen, 72% for retinal pigment epithelial degeneration, 74% for increased retinal pigment, 85% for pure geographic atrophy, and 89% for exudative macular degeneration. The kappa scores varied from 0.33 for geographic atrophy to 0.60 for exudative macular degeneration. Slightly higher rates of agreement between gradings were found after dilation. CONCLUSION: These data suggest that 45 degrees nonstereoscopic fundus photographs, when graded according to a standard classification scheme, should be considered for detection of age-related maculopathy in situations where the pupils cannot be pharmacologically dilated and retinal specialists are not available to examine the fundus.
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